导　　师： 姚若河

学科专业： 080903

授予学位： 博士

作　　者： ;

机构地区： 华南理工大学

摘　　要： 能带补偿和界面态是影响半导体异质结性能的两个最关键因素,也是最本质的物理根源。本文从能带补偿和界面态两个方面对ZnO//Si异质结的电学性能进行了研究。 采用p-n扩散模型和Anderson模型讨论了n-ZnO//p-Si异质结的I-V和C-V特性。分析了n-ZnO和p-Si中掺杂浓度,能带补偿等因素对异质结性能的影响。基于Shockley p-n结模型,分析在n-ZnO//p-Si异质结耗尽区两侧n-ZnO和p-Si中平衡载流子浓度之间的关系,讨论了n-ZnO//p-Si异质结的内建电势对光电压的影响,并给出了n-ZnO//p-Si异质结太阳能电池I-V特性表达式。和同质结相比,n-ZnO//p-Si异质结太阳能电池可以获得更高的开路电压, n-ZnO//p-Si这类结构的异质结可以提高太阳能电池的光电转换效率,尤其是用在聚光太阳能电池。对n-ZnO//n-Si异质结理想状态下I-V和C-V特性进行了研究,由于n-ZnO与n-Si两种半导体的费米能级的相对位置不同,构成的n-ZnO//n-Si异质结表现出两种完全相反整流特性。 在细致平衡理论基础上,针对异质结电池在结处由于能带不连续而形成载流子运动势垒可能对光生载流子的运输存在阻碍作用,建立了异质结太阳能电池的光电转换模型,给出了基于细致平衡理论的异质结太阳能电池的极限效率的计算方法,推导出n-ZnO//p-Si异质结太阳能电池光照下的I-V特性表达式以及最大光电转换效率的求法,并求出在理想情况AM1.5的光照下n-ZnO//p-Si异质结太阳能电池最大转换效率可达到29/%。 由于ZnO//Si异质结界面处由于晶格不匹配而形成大量的界面态。CuI和CuSCN是分子晶体,物质特性比较柔软,虽然CuI、CuSCN的热膨胀系数不同,但分别与与Si和ZnO形成异质结时界面处不会产生较大应力,不会有大量位错和缺陷形成,不会产生大量界面态。为了更好地研究CuI和CuSCN薄膜的钝化作用,分别制备了n-ZnO//p-CuI、p-CuI//n-Si和p-CuSCN//n-Si异质结,其中CuI和CuSCN薄膜是采用连续离子层沉积法制备的,n-ZnO薄膜是化学浴法制备。制备的n-ZnO//p-CuI异质结二极管具有良好的整流特性,3V正反电压下测量的整流比达600。理想因子与制备的n-ZnO//p-Si异质结相比,理想因子要小很多,说明界面态小很多。制备p-CuI//n-Si和p-CuSCN//n-Si异质结都具有良好的整流特性和光电效应。 采用磁控溅射法制备的ZnO//Si异质结具有良好的整流特性和光电效应,分别插入CuI和CuSCN界面钝化层能够减小ZnO//p-Si异质结的界面态,其中CuI效果最好,几乎不形成界面态,测量的表观内建电势与运用功函数计算的内建电势接近。插入CuI和CuSCN薄膜能够提高ZnO//p-Si异质结的整流比。但是对于ZnO//n-Si异质结,插入CuI和CuSCN界面钝化层后,由于降低了生长的ZnO薄膜的质量,从而无法提高异质结的电性能。 Band offset and interface state of the semiconductor heterostructures are the two most critical factors in performance, but also the most essential physical roots. In this paper, the ZnO//Si heterojunction electrical properties were studied from two aspects of the interface state and band offset. In this work, in order to reveal the conduction mechanism of ZnO//Si heterojunction, the voltage-current and capacitance–voltage characteristics of the ZnO//p-Si heterojunction in ideal conditions are investigated base on the p-n junction diffusing model and the Anderson diffusing model, the effects of doping concentration, working temperature and band offset on the voltage-current and capacitance–voltage characteristics are analyzed. According to the p-n junction model of Shockley, the relationship between the equilibrium carrier concentrations for n-type and p-type semiconductors on the edges of the depletion region for an n-ZnO//p-Si heterojunction solar cell is analyzed. The relationship between the photovoltage and built-in voltage for n- ZnO//p-Si heterojunction solar cell is discussed, and the expression of the total I-V characteristic is given. Using n-ZnO//p-crystalline Si heterojunction structure may improve photoelectric conversion efficiency of solar cells, especially in light-gathering solar cells. The voltage-current and capacitance–voltage characteristics of the ZnO//n-Si heterojunction in ideal conditions are investigated. Because of the difference of the Fermi level relative position, the ZnO//n-Si heterojunction shows two different rectifying behaviors. Based on detailed balance theory and considered the barriers at interface of heterojunction which result from the band offset and block photon-generated carriers transport, a photoelectric conversion model for n-ZnO//p-Si heterojunction solar cells is established. The problem of the limit efficiency of heterojunction solar cells can not be calculated using the detailed balance theory is solved. A method to realize the I-V characteristics of the n-ZnO//p- Si heterojunction solar cells under the illumination and the limit conversion efficiency of n-ZnO//p-Si heterojunction solar cells is proposed in this work. It is shown that a theoretical efficiency limit of 29/% can be achieved for n-ZnO//p-Si heterojunction solar cells under AM1.5 illumination. Because of the ZnO // Si heterojunction interface lattice mismatch, a large number of interface states are formed. The CuSCN and CuI are molecular crystals, and soft material properties. Although the CuI and CuSCN have different coefficients of thermal expansion, compare with the Si and ZnO, respectively, but when the heterojunction is made, it do not have a greater stress, not a large number of dislocations, and defects formation at the interface and not produce a large number of interface states. In order to understand the effect of passivated defects with the CuI and CuSCN thin interlayer in an even better fashion, the p-CuI//n-ZnO, p-CuI//n-Si and p-CuSCN//n-Si heterojunction has been prepared by chemical method. The CuI and CuSCN films are prepared by the successive ionic layer adsorption and reaction /(SILAR/) technique and the ZnO film is prepared by the chemical bath deposition /(CBD/). The p-CuI//n-ZnO heterojunction shows a good rectifying behavior with a rectification ratio～600 at 3 V. The p-CuI//n-Si and p-CuSCN//n-Si heterojunction show a good rectifying behavior and a good photoelectrical effect. The n-ZnO//Si heterojunction prepared by magnetron sputtering shows a good rectifying behavior and a good photoelectrical effect. The high density interfacial state at the ZnO//Si interface is reduced by the CuI and CuSCN thin interlayer between the Si substrate and the ZnO film. The effect of passivated defects with CuI film is better. By a comparison of the n-ZnO//p-Si heterojunction properties, the n-ZnO//CuI//n-Si and n-ZnO//CuSN//n-Si heterojunction show improved electrical properties, with a fairly low leakage current and high rectification ratio. But for n-ZnO//n-Si heterojunction, the electrical properties are not improved by inserting CuI and CuSCN thin interlayer.

关 键 词： 异质结 光伏 伏安特性 内建势垒

分 类 号： [O472]

领　　域： [理学] [理学]